1. Field of the invention
The present invention relates to a throttle-opening detecting apparatus which detects the rotation angle of a throttle grip mounted on a handle bar in a vehicle such as a two-wheeled vehicle to thereby detect a throttle-opening.
2. Description of the Related Art
A throttle-opening detecting apparatus for use in a two-wheeled vehicle is structured such that it detects the rotation angle of a throttle grip mounted on a handle bar and transmits a detect signal representing the thus-detected rotation angle to an electronic control unit carried on board the two-wheeled vehicle. In accordance with the detect signal, the electronic control unit carries out a given operation and, in accordance with the result of the operation, the ignition timing of an engine or the opening and closing of an exhaust valve is controlled.
A conventional throttle-opening detecting apparatus, for example, as disclosed in JP-A-4-254278, comprises mainly a drive pulley movable together with a throttle grip and rotatable in the same direction as the throttle grip, a drive gear formed in the lower portion of the drive pulley, a detecting gear rotatable in meshing engagement with the drive gear, and a potentiometer for detecting the rotation angle of the detecting gear; and, these drive pulley, drive gear, detecting gear and potentiometer are incorporated in a case fixed to a handle bar.
In this structure, in case where the throttle grip is rotated, not only the drive pulley is worked with the rotation of the throttle grip but also the detecting gear in meshing engagement with the drive gear formed in the lower portion of the drive pulley is rotated. The potentiometer detects the rotation angle of the detecting gear to thereby detect the rotation angle of the throttle grip, that is, the throttle-opening, and transmits the detected value to an electronic control unit.
On the other hand, one end of a throttle wire is fixed to the drive pulley and thus, in case where the drive pulley is rotated with the rotation of the throttle grip, the throttle wire is pulled by the drive pulley to thereby be able to operate a throttle valve connected to the other end of the throttle wire.
However, in the above-mentioned conventional throttle-opening detecting apparatus, since only the detected values are transmitted to the electronic control unit to thereby control the ignition timing of an engine and the opening and closing of an exhaust valve, the connection of the throttle-opening detecting apparatus to the throttle valve requires the throttle wire. The throttle wire can be operated so as to be pulled by the drive pulley due to the rotation of the drive pulley; and, therefore, when the throttle wire is in operation, excessive tension is applied to the throttle wire, which raises a problem that the throttle wire can be cut easily.
Also, since the throttle wire slides within an outer tube to transmit the operation of the drive pulley to the throttle valve, there arises a problem that, in case where the operating oil within the outer tube runs out, the operation of the throttle wire becomes heavy. In view of this, in case where a signal detected by the throttle-opening detecting apparatus is transmitted to the electronic control unit and the opening and closing of the throttle valve is controlled in accordance with the value operated by the electronic control unit, the throttle wire can be omitted, which makes it possible to solve the problem caused by the throttle wire.
However, in case where the throttle wire is omitted, there arises another problem that there can be obtained almost no load when rotating the throttle grip, thereby giving a driver a strange feeling. That is, in case where there is no load at all for pulling the throttle wire, the throttle grip can be rotated with a very light rotation force, which rather makes it difficult to adjust the rotation quantity of the throttle grip.